- Genetic Disorders Symptoms & Causes
- What are the physical signs of genetic disorders?
- What is genetic counseling and how do I know if I need it?
- Information About 5 Common Genetic Disorders
- Down Syndrome
- Cystic Fibrosis
- Tay-Sachs disease
- Sickle Cell Anemia
- Learn More
- Genetic disorders
- How does the diagnosis of a genetic disorder affect my pregnancy?
- How does a genetic disorder affect my baby?
- How are genetic disorders treated?
- Will I be able to help care for my baby?
- When can my baby go home?
- Medical Genetics: Types of Genetic Changes
- What are chromosome abnormalities?
- What are single-gene changes?
- How genetic changes are passed along in a family
- Getting genetic testing
- Genes and human diseases
Genetic Disorders Symptoms & Causes
What are the physical signs of genetic disorders?
The following list includes features that might suggest that your child has a genetic disorder. However, some of these characteristics are commonly found in people without a disorder. You’ll want to check with you doctor if your child has at least two of the following features:
- Ear abnormalities
- Unusually shaped eyes
- Different colored eyes
- Facial features that are unusual or different from other family members
- Brittle or sparse hair
- Excessive body hair
- White patches of hair
- Large or small tongue
- Misshapen teeth
- Missing or extra teeth
- Loose or stiff joints
- Unusually tall or short stature
- Webbed fingers or toes
- Excessive skin
- Unusual birthmarks
- Increased or decreased sweating
- Unusual body odor
What is genetic counseling and how do I know if I need it?
Genetic counseling can tell you whether you’re at risk of developing a genetic disorder or having a child with a genetic disorder. Genetic counseling can also help you to make sense of the information and put it into context for your child. It may be conducted by a geneticist, a doctor with special training or a genetic counselor, who will explain the cause of a disorder, availability of testing, prognosis, medical management and treatment. Genetic counseling sessions typically last an hour or longer, depending on the complexity of your child’s case is. There are many reasons to seek genetic counseling, including the following:
1. Family history or previous child with:
- chromosome abnormalities (such as Down syndrome)
- cleft lip/palate
- heart defects
- mental retardation
- neural tube defects
- short stature
- single gene defects (such as cystic fibrosis or PKU)
- hearing or visual impairments
- learning disabilities
- psychiatric disorders
- multiple pregnancy losses (miscarriages, stillbirths or infant deaths)
2. A parent with an autosomal dominant disorder, or any disorder seen in several generations
3. Pregnancy factors (mother older than 35 years)
4. Mother with any of the following:
- thyroid disorder
- fetal or parental exposure to certain drugs, chemicals, radiation or infections
- advanced paternal age at the time of conception
- infertility cases where either parent is suspected of having a chromosome abnormality
- couples requiring assisted reproductive techniques to achieve a pregnancy, or individuals donating eggs or sperm for those purposes
- Ethnic groups or geographic areas with a higher incidence of certain disorders, such as Tay Sachs disease, sickle cell disease or thalassemias
Information About 5 Common Genetic Disorders
Genetic disorders can be the result of genetic abnormalities such as gene mutation or additional chromosomes. The effects of abnormalities in an individual’s DNA were once entirely unpredictable. However, modern medicine has produced methods of identifying the potential health outcomes of genetic disorders, as evidenced by medical research from educated, advanced-degreed nurse practitioners and practicing physicians. By collecting the following evidence-based statistical observations, these professionals have identified some of the current best practices for detecting, treating, and potentially preventing some genetic disorders.
Typically, the nucleus of an individual cell contains 23 pairs of chromosomes, but Down syndrome occurs when the 21st chromosome is copied an extra time in all or some cells. Nurse practitioners and physicians commonly perform detailed prenatal screening tests, like blood tests, that detect quantities of chromosomal material and other substances in a mother’s blood. This type of testing can determine, with high accuracy, whether or not a child will be born with Down syndrome. When a person is diagnosed with Down syndrome, they are likely to exhibit varying levels of mild to severe cognitive delays. Other markers of Down syndrome include a higher disposition for congenital heart defects, low muscle tone, smaller physical stature, and an upward slant to the eyes. According to the Centers for Disease Control and Prevention (CDC), approximately one in every 700 babies born in the US will have Down syndrome. Also, the older a mother is at the time of birth, the more likely the child is to have Down syndrome.
Thalassemia is a family of hereditary genetic conditions that limits the amount of hemoglobin an individual can naturally produce. This condition inhibits oxygen flow throughout the body. There is a 25 percent chance that children who inherit the Thalassemia gene from both parents will be born with Thalassemia. People who are especially likely to be carriers of the faulty gene that is responsible for Thalassemia include those of Southeast Asian, Indian, Chinese, Middle Eastern, Mediterranean, and Northern African descent. With any form of Thalassemia usually comes severe anemia, which may require specialized care such as regular blood transfusions and chelation therapy.
Cystic Fibrosis is a chronic, genetic condition that causes patients to produce thick and sticky mucus, inhibiting their respiratory, digestive, and reproductive systems. Like Thalassemia, the disease is commonly inherited at a 25 percent rate when both parents have the Cystic Fibrosis gene. In the United States, there are close to 30,000 people living with Cystic Fibrosis, and they frequently develop greater health problems. For instance, 95 percent of male Cystic Fibrosis patients are sterile, and the median age of survival for all patients is 33.4 years. Educated nurse practitioners can extend the typical patient’s survival time by offering effective care strategies that feature physical therapy, as well as dietary and medical supplementation.
The genetic condition known as Tay-Sachs is carried by about one in every 27 Jewish people, and by approximately one of every 250 members of the general population. The condition is caused by a chromosomal defect similar to that of Down syndrome. Unlike Down syndrome, however, Tay-Sachs results from a defect found in chromosome #15, and the disorder is irreversibly fatal when found in children. Tay-Sachs disease gradually destroys the nervous system, frequently resulting in death by age five. Adults can also be diagnosed with Late-Onset Tay-Sachs disease, which causes a manageable level of diminished cognitive ability. While detecting Tay-Sachs can be accomplished by using enzyme assay methods or DNA studies, an option does exist to prevent the risk entirely. Assisted reproductive therapy techniques can be conducted that test in-vitro embryos for Tay-Sachs before implanting them into the mother. This can allow only healthy embryos to be selected.
Sickle Cell Anemia
Sickle Cell Disease is a lifelong genetic condition that may be inherited when the Sickle Cell trait is passed down by both parents to their children. The trait is more commonly inherited by people with a sub-Saharan, Indian, or Mediterranean heritage. Sickle Cell Disease causes red blood cells to change from their usual donut shape to a sickle shape. This causes the cells to clump together and become caught in blood vessels, triggering severe pain and serious complications such as infections, organ damage, and acute respiratory syndrome. According to the CDC, Sickle Cell Disease affects approximately 100,000 Americans. Additionally, one in every 365 African-American babies is born with Sickle Cell Disease. In contrast, one in every 16,300 Hispanic-American babies is diagnosed with the disease. Modern advancements in medicine have limited the mortality rate of Sickle Cell Disease by providing a greater variety of vaccines and treatment options.
Giving birth to a child with a genetic condition can be concerning for parents, but effective ongoing care from trained nursing professionals can significantly ease the impact. Through a Doctor of Science in Nursing program, nurse practitioners can expand their knowledge and practical ability to confront and mitigate these disorders. By adding new expertise in the leading-edge detection, prevention, and treatment of genetic disorders, advanced-degreed nurses can play a key role in helping parents, children, adult sufferers, and society at large.
Health care is a dynamic and ever-evolving field, and more is now expected of nurse leaders. In fact, the American Association of Colleges of Nursing (AACN) has called for a doctoral level education to become the requirement for advanced practice nursing. Earning an online Doctor of Nursing Practice (DNP) puts MSN-credentialed nurses like you at the forefront of the industry — prepared for leadership, nurse education, patient care, and to shape future policies and procedures in health care.
How Family Nurse Practitioners With a DNP Degree Empower Patients and Families
1. NIH – How are genetic conditions treated or managed?
2. NIH – What information about a genetic condition can statistics provide?
3. NIH – Genetic Disorders
4. National Human Genome Research Institute
5. National Down Syndrome Society
6. Centers for Disease Control and Prevention – Down Syndrome
7. The Demographics of Thalassemia
9. Cystic Fibrosis News Today
10. National Human Genome Research Institute – Learning About Tay-Sachs Disease
11. Centers for Disease Control and Prevention – Sickle Cell Disease
12. Centers for Disease Control and Prevention – Incidence of Sickle Cell Trait in the US
How does the diagnosis of a genetic disorder affect my pregnancy?
What do you do if the test results come back with information you were not expecting, such as your baby has a genetic disorder or birth defect? By knowing the diagnosis before delivery you are given time to process the information, research the care options, and make informed decisions. This does not make the decisions easier, but it gives you time to be more involved in the decisions that will need to be made. You can get input from family, pastors/priests, friends, and medical professionals. You can be an informed decision maker who is actively involved in all aspects of your baby’s care. We will be here to provide information at whatever pace you desire, in whatever way is most beneficial to you.
How does a genetic disorder affect my baby?
Listed below is a brief description of some of the more common genetic/chromosomal defects that may be diagnosed prenatally.
Trisomy 13 means there are three number 13 chromosomes rather than the usual two. Trisomy 13 has a reported incidence of 1 in 2,200 to 7,600 live births. This chromosomal defect is associated with major congenital anomalies. The most common of which include: holoprosencephaly (the two cerebral hemispheres are fused) or other central nervous system abnormalities, abnormal midface development including clefting, and congenital heart defect. Many fetuses with Trisomy 13 die before they reach term and/or are miscarried. Fifty to eighty percent of infants with Trisomy 13 that are born alive will die by the age of 1 month and 75 to 90 percent have died by age 6 months. Very rarely, affected persons have survived to adulthood.
Trisomy 18 is a term used to describe the presence of three number 18 chromosomes rather than the usual two. Trisomy 18 has a reported incidence of 1 in 3,000 to 7,000 live births. This chromosomal defect is associated with major congenital anomalies. The most commonly associated abnormalities include: intrauterine growth restriction, cardiac defects, club foot/feet or rocker bottom feet, and omphalocele. Cranial abnormalities are seen with trisomy 18. These abnormalities include: an unusually shaped head with a wide occipitoparietal and narrow frontal diameter, which has also been described as the “strawberry sign” because of the shape of the head view on ultrasound. Several studies reviewed demonstrated 50% of babies with Trisomy 18 had died by one week of age, and 90 percent by six months. There is a small percentage that will survive beyond infancy. Females are more likely to survive (although not for an extended length of time) than males and the disorder is seen more often in females than males (3:1).
Trisomy 21 is a term used to describe the presence of three number 21 chromosomes rather than the usual two. Another name for trisomy 21 is Down syndrome. Down syndrome has a reported incidence of 1 in 800 live births, however the risk of incidence increases with advanced maternal age. The most commonly seen congenital abnormalities include: cystic hygroma (abnormal fluid accumulation around the neck area), nuchal-fold thickness (skin on the back of the neck is thicker than normal), hydrops (abnormal fluid accumulation in two areas of the body such as around the heart, around the lungs, in the abdomen or under the skin), cardiac defects, renal hydronephrosis (part of the kidney has abnormal collection of fluid) and skeletal (bone) abnormalities.
Klinefelter syndrome (47,XXY karyotype)
These are male infants with an extra X chromosome. Many will go undiagnosed until maturity as adults undergoing infertility workups. Fetuses are typically identified during amniocentesis performed for advanced maternal age. They are not normally identified because of an abnormal ultrasound finding. Some information typical of Klinefelter syndrome includes:
- Sons are typically taller than normal (In the 75th percentile on growth charts).
- Puberty will be entered normally but may consider testosterone supplementation therapy after mid-adolescence.
- Sons are infertile.
- Sons are at risk for developmental problems and speech, neuromotor and learning delays.
Achondroplasia is an autosomal dominant genetic disorder of bone growth. It affects 1 in 25,000 live births and occurs equally in both sexes and all races. Affected individuals have short arms and legs with a normal torso size. The head is usually large, sometimes due to hydrocephalus, and the forehead is prominent. Achondroplasia is the result of an abnormal gene located on one of the chromosome 4 pair. Eighty percent of these cases are not inherited. Both parents are normal size with normal chromosome 4, but a new mutation occurs for an unknown reason. If one parent has the condition and the other parent does not, their offspring have a 50 percent percent chance of being affected. If both parents have achondroplasia, they have a 50 percent chance of their offspring inheriting the condition, 25 percent chance of not inheriting the condition, and a 25 percent chance of inheriting the abnormal gene from both parents, which results in severe skeletal abnormalities that lead to an early death.
Tay-sachs is an inherited disease of the central nervous system that is incompatible with life. A Tay-Sachs carrier has one normal gene and one Tay-Sachs gene making it an autosomal recessive disease. It occurs most frequently in central and eastern European descendants, (Ashkenazi) Jews. Approximately 1 in every 30 American Jews is a carrier of the Tay-Sachs gene. The carrier leads a normal, healthy and full life. Both parents would need to be carriers and each would contribute the affected gene to have an affected baby. A baby with Tay-sachs will appear normal at birth and for approximately 4 to 6 months. The affected baby lacks an enzyme necessary for breaking down certain fatty substances in the brain and nerve cells. At a few months of age the baby will gradually stop smiling, crawling or turning over. Eventually they lose their ability to grasp or reach out and become blind and paralyzed. Death occurs by age 5. If both parents are carriers of Tay-Sachs, their offspring have a 50 percent chance of being a carrier for Tay-sachs; a 25 percent chance of contracting the disease by receiving a defective gene from each parent; and a 25 percent chance of inheriting normal genes from each parent.
Phenylketonuria (PKU) is an autosomal recessive, inherited disorder of body metabolism. Metabolism is the process of breaking down food to be used by the body. An affected individual lacks an enzyme necessary to process the protein, phenylalanine. Without treatment this protein builds up in the bloodstream and causes mental retardation. Treatment involves following a special diet that is low in phenylalanine. Since the 1960s, all newborns born in the United States are screened for this disorder shortly after birth. Approximately 1 in every 15,000 babies born is affected. Both parents of these newborns are carriers, but are unaffected. Their offspring have a 50 percent chance of being carriers; 25 percent chance of being affected or inheriting the defective gene from both parents; and a 25 percent chance of inheriting only normal genes from his/her parents. The affected baby appears normal at birth but will develop symptoms of listlessness and lose interest in their surroundings by age 3 to 6 months. The issue today is females who have been diagnosed in infancy with the disease who are now having babies. These women may have begun to eat a normal diet and no longer follow the phenylalanine restrictions. The result is a very high level of phenylalanine in their blood, which can be devastating to their offspring. These women should be counseled prenatally to resume the special diet for at least three months prior to conception and throughout their pregnancy to prevent defects in their babies.
Cystic fibrosis (CF)
Cystic fibrosis (CF) is an autosomal recessive, inherited disorder that affects breathing and digestion. There is no cure. Both parents are carriers but are unaffected. A child with CF has inherited a defective gene from each parent. Future offspring have a 50 percent chance of becoming a carrier or inheriting the defective gene from one parent; a 25 percent chance of being affected; and a 25 percent chance of inheriting only normal genes. With cystic fibrosis the pancreas and lungs are most affected. Mucus and other secretions become thick and sticky. This thick mucous can clog the lungs and causes breathing problems and frequent lung infections, which eventually damages the lungs. The thickened secretions made by the pancreas for digestion of food, are unable to reach the small intestine. This can lead to digestive problems including inability to gain weight or grow at a normal rate. The symptoms of cystic fibrosis will range from mild to severe. Some will attend school and college and participate in some exercise, while others are too ill to attend school regularly. Males affected by CF are commonly infertile and females have reduced fertility. Cystic fibrosis does not affect a person’s appearance or intelligence. Most affected individuals survive to 30 or 40 years of age.
Fragile X syndrome
Fragile X syndrome is the most common inherited form of mental retardation in males. It affects 1 in 4,000 males and 1 in 8,000 females. In 1991, a researcher discovered a “mutation” in a gene located on the X chromosome, as the cause of the Fragile X syndrome. Mutation means the addition or deletion of genetic material. A small section of the genetic material at this location is repeated too many times. Normally there are 6 to 40 repeats of this section. If there are 60 to 200 repeats, this is a pre-mutation, and greater than 200 repeats is a mutation. With a mutation the gene will “turn off” and not produce the protein that it normally would make. The lack of this specific protein causes the symptoms of fragile X syndrome. A pre-mutation carrier mother has a 50 percent chance of passing on the abnormal gene to her offspring. Males are generally more severely affected because they have only one X chromosome and one Y chromosome, as compared to a female who has two X chromosomes. As this defective gene is passed on it is likely to expand in the number of repeats and become a full mutation. A man can also be an unaffected carrier of a pre-mutation fragile X gene. This male will pass on the pre-mutation (does not usually expand) to all his daughters but to none of his sons. These daughters generally have no symptoms, but are carriers and may pass it on to their children. Affected individuals have varying degrees of mental retardation or learning disabilities and behavioral and emotional problems, including autistic-like features.
Turner syndrome affects only females. It occurs when one of the two X chromosomes normally found in females is missing or incomplete. This, at present, appears to be a random event with no known cause. Turner syndrome is among the most common chromosomal abnormalities affecting 1 in every 2,500 live female births. Most affected females will have normal intelligence. However, 10 percent will have substantial delays and as many as 70 percent will have some mild delays such as learning disabilities. It is believed these women can lead a full and productive life with regular, competent medical care. The most common characteristics of a female with Turner syndrome includes short stature and lack of ovarian development. They are also prone to cardiovascular, kidney and thyroid problems as well as skeletal disorders (scoliosis) and ear and/or hearing disturbances.
How are genetic disorders treated?
Treatment is completely dependent on the disorder or syndrome, the prognosis of the disorder and parental wishes. Some disorders have very short life expectancies for which treatment would not be beneficial. However, some children with genetic disorders can and do function well with normal life expectancies. Others can be variable depending on the associated birth defects. For example, some Trisomy 21 babies can go home from the newborn nursery with minimal problems and others have multiple congenital anomalies that require numerous surgeries and more than one system can be affected. The treatment for these babies will be a collaborative effort of providing information as accurately as we can and allowing you, as the parent, to be the primary decision makers about the care to be provided.
Will I be able to help care for my baby?
Yes! Please ask your baby’s nurse about ways to interact with and care for your baby.
If you had planned on breastfeeding your baby, and the baby is unable to eat immediately after birth, you can express your milk while you are still in the hospital. A lactation consultant can assist in answering your questions. Your milk will be frozen until your baby is ready for it. The Birth Center and Neonatal Intensive Care Unit (NICU) have breast pumps available to you when you are in the hospital or visiting. You can bring in pictures, small toys, booties, and blankets for your baby if he/she is in the NICU.
When can my baby go home?
Your baby will go home when you and the medical professionals have deemed it appropriate. Some of these genetic disorders have a short life expectancy. If you are ready to go home and desire to take your baby home with you, knowing they will not have a long-term survival, arrangements can be made for you to continue to care for your baby at home. There are home health services or hospice care that can assist you with care in the home. Some of these babies may have conditions that require surgical repair before he/she can go home. This will prolong the hospital stay for your baby. Some genetic disorders may go undiagnosed for months to years if symptoms are mild. Many of these babies go home from the newborn nursery without any problems until later in life.
Learn more about the Genetics Center at Children’s Hospital of Wisconsin, which works in partnership with the Fetal Concerns Center.
Medical Genetics: Types of Genetic Changes
The human body has about 20,000 different genes in each cell. Genes are located on chromosomes, which are stick-shaped structures in the middle of the cell (nucleus) . Each cell usually has 46 chromosomes grouped in 23 pairs. Each gene has a specific function. And when a gene or chromosome is abnormal, it may cause health problems in the body.
There are 2 main types of genetic changes:
What are chromosome abnormalities?
Chromosome abnormalities in the baby may be inherited from the parent or may occur with no family history. These are the most common:
This means there are more or fewer chromosomes than the normal number. Examples include:
Down syndrome (trisomy 21). Cells contain 3 copies of the 21st chromosome.
Turner syndrome. One of the 2 sex chromosomes is not transferred. This leaves a single X chromosome for 45 total chromosomes instead of 46.
This is when part of a chromosome is missing, or part of the DNA code is missing.
This is when a chromosome breaks and the piece of it turns around and reattaches itself. Inversions can be passed down in families, but they may or may not cause birth defects.
A ring chromosome is one where the ends are attached to itself to form a ring. Rings can be passed down in families. They may or may not cause health problems.
This is when a chromosome segment rearranges from one location to another. It can happen either within the same chromosome or move to another chromosome. There are 2 types:
Balanced translocation. This is when the DNA is equally exchanged between chromosomes. No DNA is lost or added. A parent with a balanced translocation is healthy, but he or she may be at risk for passing on unbalanced chromosomes to a child.
Robertsonian translocation. This is a balanced translocation in which 1 chromosome joins the end of another.
This is when a person has 2 or more sets of chromosomes in his or her cells with different genetic material.
What are single-gene changes?
A change in a single gene causes a defect or abnormality. Single-gene changes usually have a higher risk of being passed on to children. Single-gene changes can be:
This means the abnormality occurs when only 1 of the genes from 1 parent is abnormal. If the parent has the disorder, the baby has a 1 in 2 chance of inheriting it. Examples include:
Achondroplasia. This is a bone development disorder that causes dwarfism.
Marfan syndrome. This is a connective tissue disorder that causes long limbs and heart defects.
This means the abnormality only occurs when both parents have a copy of an abnormal gene. If both parents are carriers, a baby has a 1 in 4 chance of having the disorder. Examples include:
Cystic fibrosis. This is a disorder of the glands that causes excess mucus in the lungs. It also causes problems with how the pancreas works and with how food is absorbed.
Sickle cell disease. This condition causes abnormal red blood cells that don’t carry oxygen normally.
Tay-Sachs disease. This is an inherited condition that causes the central nervous system to decline. The condition is fatal, usually by age 5.
The disorder is determined by genes on the X chromosome. Males are mainly affected and have the disorder. Daughters of men with the disorder are carriers of the trait and have a 1 in 2 chance of passing it to their children. Sons of women who are carriers each have a 1 in 2 chance of having the disorder. Examples include:
Duchenne muscular dystrophy. This is a disease that causes muscle wasting.
Hemophilia. This is a bleeding disorder caused by low levels or lack of a blood protein that is needed for clotting.
How genetic changes are passed along in a family
The way a gene is inherited can help determine the risk of it in a current or future pregnancy. The risk of having a baby with a birth defect from a genetic change increases if:
The parents have another child with a genetic disorder.
There is a family history of a genetic disorder.
One parent has a chromosome abnormality.
The baby in the womb has abnormalities seen on an ultrasound.
Families at risk for genetic diseases may want to talk with a certified genetic counselor. Making a chart of the family members and their health histories can help show risks for certain problems. Genetic counseling also helps parents understand the effects of a disorder and ways it may be prevented or treated.
Getting genetic testing
Each parent’s DNA may need to be checked. This is done to learn about some genetic inheritance patterns. Prenatal testing can also be done to check the baby in the womb for problems. Testing may include:
Ultrasound. This test uses sound waves to look at how a baby in the womb is growing.
Chorionic villus sampling (CVS). This test uses a sample of tissues around the baby to look for problems.
Amniocentesis. This test uses a sample of the amniotic fluid from the sac around the baby to check for problems.
Noninvasive prenatal screening. This test involves taking a blood sample from the mother to look for chromosome differences, such as aneuploidy.
Carrier screening. This test uses a sample of blood from each parent to check if they carry genetic changes for certain genetic conditions.
Genes and human diseases
Monogenic diseases result from modifications in a single gene occurring in all cells of the body. Though relatively rare, they affect millions of people worldwide. Scientists currently estimate that over 10,000 of human diseases are known to be monogenic. Pure genetic diseases are caused by a single error in a single gene in the human DNA. The nature of disease depends on the functions performed by the modified gene. The single-gene or monogenic diseases can be classified into three main categories:
All human beings have two sets or copies of each gene called “allele”; one copy on each side of the chromosome pair. Recessive diseases are monogenic disorders that occur due to damages in both copies or allele. Dominant diseases are monogenic disorders that involve damage to only one gene copy. X linked diseases are monogenic disorders that are linked to defective genes on the X chromosome which is the sex chromosome. The X linked alleles can also be dominant or recessive. These alleles are expressed equally in men and women, more so in men as they carry only one copy of X chromosome (XY) whereas women carry two (XX).
Monogenic diseases are responsible for a heavy loss of life. The global prevalence of all single gene diseases at birth is approximately 10/1000. In Canada, it has been estimated that taken together, monogenic diseases may account for upto 40% of the work of hospital based paediatric practice (Scriver, 1995).
Sickle cell anemia
Tay sachs disease
Fragile X syndrome
Thalassaemia is a blood related genetic disorder which involves the absence of or errors in genes responsible for production of haemoglobin, a protein present in the red blood cells. Each red blood cell can contain between 240 and 300 million molecules of haemoglobin. The severity of the disease depends on the mutations involved in the genes, and their interplay.
A haemoglobin molecule has sub-units commonly referred to as alpha and beta. Both sub-units are necessary to bind oxygen in the lungs properly and deliver it to tissues in other parts of the body. Genes on chromosome 16 are responsible for alpha subunits, while genes on chromosome 11 control the production of beta subunits. A lack of a particular subunit determines the type of thalassaemia (eg. a lack of alpha subunits results in alpha-thalassemia). The lack of subunits thus corresponds to errors in the genes on the appropriate chromosomes.
There can be various gradations of the disease depending on the gene and the type of mutations.
The alpha and beta thalassaemias are the most common inherited single-gene disorders in the world with the highest prevalence in areas where malaria was or still is endemic. The burden of this disorder in many regions is of such a magnitude that it represents a major public health concern. For example in Iran, it is estimated that about 8,000 pregnancies are at risk each year. In some endemic countries in the Mediterranean region, long-established control programs have achieved 80-100% prevention of newly affected births.
Diagnosis of thalassaemia can be made as early as 10-11 weeks in pregnancy using procedures such as amniocentesis and chorionic villi sampling. Individuals can also be tested for thalassaemia through routine blood counts. Thalassaemic patients may have reduced fertility or even infertility. Early treatment of thalessaemia has proved to be very effective in improving the quality of life of patients. Currently, genetic testing and counselling, and prenatal diagnosis play an increasingly important role in informing individual as well as professional decisions around the prevention, management and treatment of this disease.
- Argentina: La Fundación Argentina de Talasemia
- Argentina: Thalassaemia Argentina
- Australia: Thalassaemia Society of Victoria
- Canada: Thalassemia Foundation of Canada
- Cyprus: Thalassaemia International Federation
- Hong Kong: Children’s Thalassaemia Foundation
- Hong Kong: Thalassaemia Society of Hong Kong
- India: Thalassemics India
- Italy: Berloni Foundation Against Thalassaemia
- Lebanon: Lebanon Chronic Care Centre
- Nigeria: Sickle Cell Foundation Nigeria
- Pakistan: Thalassaemia Society of Pakistan
- UK: North of England Thalassaemia Association
- UK: UK Thalassaemia Society
- USA: Cooley’s anemia foundation
- USA: Northern California Comprehensive Thalassemia Center
Sickle cell anemia
Sickle-cell anemia is a blood related disorder that affects the haemoglobin molecule, and causes the entire blood cell to change shape under stressed conditions. In sickle cell anaemia, the haemoglobin molecule is defective. After haemoglobin molecules give up their oxygen, some may cluster together and form long, rod-like structures which become stiff and assume sickle shape.
Unlike healthy red blood cells, which are usually smooth and donut-shaped, sickled red blood cells cannot squeeze through small blood vessels. Instead, they stack up and cause blockages that deprive organs and tissues of oxygen-carrying blood. This process produces periodic episodes of pain and ultimately can damage tissues and vital organs and lead to other serious medical problems. Normal red blood cells live about 120 days in the bloodstream, but sickled red cells die after about 10 to 20 days. Because they cannot be replaced fast enough, the blood is chronically short of red blood cells, leading to a condition commonly referred to as anemia.
Sickle cell anemia affects millions throughout the world. It is particularly common among people whose ancestors come from Sub-Saharan Africa, South America, Cuba, Central America, Saudi Arabia, India, and Mediterranean countries such as Turkey, Greece, and Italy. In the Unites States, it affects around 72,000 people, most of whose ancestors come from Africa. The disease occurs in about 1 in every 500 African-American births and 1 in every 1000 to 1400 Hispanic-American births. About 2 million Americans, or 1 in 12 African Americans, carry the sickle cell allele.
The sickle cell disease can be diagnosed in a simple blood test. In many cases, sickle-cell anemia is diagnosed when new-borns are screened. Vaccines, antibiotics, and folic acid supplements are administered, in addition to pain killers. Blood transfusions and surgery are used in severe cases. The only known cure at present is a bone marrow transplant.
- American Sickle Cell Anemia Association
- Genetics Home Reference: Sickle Cell Anemia
- MEDLINEplus: Sickle Cell Anemia
- UK : NHS Sickle Cell & Thalassaemia Screening Programme
Haemophilia is a hereditary bleeding disorder, in which there is a partial or total lack of an essential blood clotting factor. It is a lifelong disorder, that results in excessive bleeding, and many times spontaneous bleeding, which, very often , is internal. Haemophilia A is the most common form, referred to as classical haemophilia. It is the result of a deficiency in clotting factor 8, while haemophilia B (Christmas Disease) is a deficiency in clotting factor 9. This illness is a sex-linked recessive disorder.
Due to the sex-linkage of the disorder, there is a greater prominence in males than in females. About a third of new diagnoses are where there is no previous family history. It appears world-wide and occurs in all racial groups. About 6,000 people are affected with haemophilia in the UK. There are about 5400 people in the UK with haemophilia A and about 1100 with haemophilia B.
Blood tests can determine the presence of the haemophilia condition, and more specifically whether it is a type A or a type B disease. Usually, infants do not show signs before 9 months of age. Administration of clotting factors help affected individuals to live with the disease. There are various lifestyle changes that one can make as a haemophiliac, and though a serious disease, it can be tolerable with proper precautions and therapy. The prospects for youngster with haemophilia are excellent. Only a few decades ago, children with haemophilia had a significantly reduced life expectancy. They were often crippled with arthritis and joint deformity by their teens and had to attend special schools for disabled people. Many recent studies have documented a greatly increased life-expectancy among people suffering from haemophilia in developed countries over the last few decades. Children with haemophilia now face few limitations. They certainly attend normal schools, most jobs are open to them, and full participation in society through employment, marriage and having children is now the norm. It is anticipated, however, that the number of people with haemophilia in developed countries will increase steadily over the next few decades
- Canadian Hemophilia Society
- National Hemophilia Foundation, USA
- The Haemophilia Society, UK
- World Federation of Hemophilia
- Hemophilia Federation (India)
Cystic Fibrosis is a genetic disorder that affects the respiratory, digestive and reproductive systems involving the production of abnormally thick mucus linings in the lungs and can lead to fatal lung infections. The disease can also result in various obstructions of the pancreas, hindering digestion. An individual must inherit two defective cystic fibrosis genes, one from each parent, to have the disease. Each time two carriers of the disease conceive, there is a 25 percent chance of passing cystic fibrosis to their children ; a 50 percent chance that the child will be a carrier of the cystic fibrosis gene; and a 25 percent chance that the child will be a non-carrier.
The incidence of CF varies across the globe. Although it is severely underdiagnosed in Asia, existing evidence indicates that the prevelance of CF is rare. In the European Union 1 in 2000-3000 new borns is found to be affected by CF . In the United States of America the incidence of CF is reported to be 1 in every 3500 births.
People with CF have a variety of symptoms including: very salty-tasting skin; persistent coughing, at times with phlegm; wheezing or shortness of breath; an excessive appetite but poor weight gain; and greasy, bulky stools. Symptoms vary from person to person, in part, due to the more than 1,000 mutations of the CF gene, several of which have been identified and sequenced by researchers.The sweat test is the standard diagnostic test for CF. This simple and painless procedure measures the amount of salt in the sweat. A high salt level indicates CF. Although the results of this test are valid any time after a baby is 24 hours old, collecting a large enough sweat sample from a baby younger than 3 or 4 weeks old may be difficult. The sweat test can also confirm the diagnosis in older children and adults. If pancreatic enzyme levels are reduced, an analysis of the person’s stool may reveal decreased or absent levels of the digestive enzymes (trypsin and chymotrypsin) or high levels of fat. If insulin secretion is reduced, blood sugar levels are high. Pulmonary function tests may show that breathing is compromised. Also, a chest x-ray may suggest the diagnosis. Relatives other than the parents of a child with cystic fibrosis may want to know if they’re likely to have children with the disease. Genetic testing on a small blood sample can help determine who has a defective cystic fibrosis gene. Unless both parents have at least one such gene, their children will not have cystic fibrosis. If both parents carry a defective cystic fibrosis gene, each pregnancy has a 25 percent chance of producing a child with cystic fibrosis. During pregnancy, an accurate diagnosis of cystic fibrosis in the fetus is usually possible.
The severity of cystic fibrosis varies greatly from person to person regardless of age; the severity is determined largely by how much the lungs are affected. However, deterioration is inevitable, leading to debility and eventually death. Nonetheless, the outlook has improved steadily over the past 25 years, mainly because treatments can now postpone some of the changes that occur in the lungs. Half of the people with cystic fibrosis live longer than 28 years. Long-term survival is somewhat better in males, people who don’t have pancreatic problems, and people whose initial symptoms are restricted to the digestive system. Despite their many problems, people with cystic fibrosis usually attend school or work until shortly before death. Gene therapy holds great promise for treating cystic fibrosis.
- More information on CF gene therapy
According to the CF Foundation’s National Patient Registry, the median age of survival for a person with CF is currently 33.4 years. Only thirty years ago, a CF patient was not expected to reach adulthood. Many people even live into their fifties and sixties.
As more advances have been made in the treatment of CF, the number of adults with CF has steadily grown. Today, nearly 40 percent of the CF population is age 18 and older. Adults, however, may experience additional health challenges including CF-related diabetes and osteoporosis. CF also can cause reproductive problems – more than 95 percent of men with CF are sterile. But, with new technologies, some are becoming fathers. Although many women with CF are able to conceive, limited lung function and other health factors may make it difficult to carry a child to term.
- Cystic Fibrosis Worldwide
- Cystic Fibrosis Foundation, USA
- Cystic Fibrosis.com
- Canadian Cystic Fibrosis Foundation, Canada
- Cystic Fibrosis Trust, UK
Tay sachs disease
Tay-Sachs disease is a fatal genetic disorder in which harmful quantities of a fatty substance called Ganglioside GM2 accumulate in the nerve cells in the brain. This is caused by a decrease in the functioning of the Hexosaminidase A enzyme. Abnormal Hexosaminidase A enzyme activity causes an accumulation of fat in nerve cells, leading to paralysis, dementia, blindness, psychoses, and even death. Though the degradation of the central nervous system begins at the fetal stage, observations such as loss of peripheral vision and motor co-ordination are not seen until about 6 months of age. This disease is autosomal recessive which means that an individual must inherit two defective genes, one from each parent, to inherit this disease. According to the age of onset there are two existing forms of Tay-Sachs disease.
- Infantile Tay-Sachs disease
- Late onset Tay-Sachs disease ( chronic GM2-gangliosidosis)
The frequency of the condition is much higher in in Ashkenazi Jews of Eastern European origin than in others.
Approximately one in every 27 Jews in the United States of America is a carrier of the TSD gene. There is also a noticeable incidence of TSD in non-Jewish French Canadians living near the St. Lawrence River and in the Cajun community of Louisiana. By contrast, the carrier rate in the general population as well as in Jews of Sephardic origin is about one in 250.
Among Jews of Sephardic origin and in the general, non-Jewish population, the carrier rate is about 1 in 250. There are certain exceptions. French-Canadian and the Cajun community of Louisiana have the same carrier rate as Ashkenazi Jews, one in 27. Also, individuals with ancestry from Ireland are at increased risk for the Tay-Sachs gene. Current research indicates that among Irish Americans, the carrier rate is about one in 50.
The diagnosis for Tay- Sachs disease (TSD) can be made via a blood test in which the Hex A enzyme can be measured in either the serum, the white blood cells, or in the skin fibroblast. Over the past 25 years, carrier screening and genetic counselling within high-risk populations have greatly reduced the number of children born with TSD in these groups. Therefore, a great percentage of the babies born with Tay-Sachs Disease today are born to couples who were not previously thought to be at significant risk.
Prenatal tests that can diagnose Tay-Sachs in the fetus before birth are available. These procedures are referred to as Amniocentesis and Chorionic Villus Sampling. Amniocentesis sampling is performed between the 15th and 16th week of pregnancy. The procedure involves inserting a needle into the mother’s abdomen and obtaining a sample of the fluid that surrounds the baby. In Chorionic Villus Sampling a sample of cells from the placenta is retrieved by the doctor during the 10th and 12th week of pregnancy, and tested for the presence of Hex A.
- National Institute of Neurological Disorders and Stroke: Tay-Sachs Disease Information page (USA)
The Fragile X syndrome is caused by a “fragile” site at the end of the long arm of the X-chromosome. It is a genetic disorder that manifests itself through a complex range of behavioural and cognitive phenotypes. It is the result of genetic mutation which varies considerably in severity among patients. Fragile X syndrome is the most common cause of inherited mental retardation. Although it is a X-linked recessive trait with variable expression and incomplete penetrance, 30% of all carrier women are affected.
According to the Fragile X association of Southern California, Fragile X syndrome is the single most common inherited cause of mental impairment affecting 1 in 3600 males and 1 in 4000 to 6000 females with full mutation worldwide. Some studies also suggest that fragile X affects 1 in every 2000 males and 1 in every 4000 females of all races and ethnic groups. Studies have also revealed that 1 in 259 women of all races carry fragile X and could pass it to their children. The number of men who are carriers is thought to be 1 in 800 of all races and ethnicity. Carrier females have a 30% to 40>% chance of giving birth to a retarded male child and a 15 to 20% chance of having a retarded female.
The diagnosis of Fragile-X syndrome is made through the detection of errors in the FMR1 gene. Over 99% of individuals have a full mutant FMR1 gene. Tests used for diagnosis include chromosome analysis and various protein tests. Diagnosis is usually made when young, and there is no current cure for this illness. Early diagnosis of the syndrome call allow for therapeutic interventions like speech therapy, occupational therapy, psychotherapy and special education, that can considerably improve the quality of the patients’ life.
- FRAXA Research Foundation, USA
- The National Fragile X Foundation
Huntington’s disease is a degenerative brain disorder, in which afflicted individuals lose their ability to walk, talk, think, and reason. They easily become depressed, and lose their short-term memory capacity. They may also experience a lack of concentration and focus. This disease begins between ages 30-45, and every individual with the gene for the disease will eventually develop the disease. Huntington’s is an autosomal dominant genetic disorder which means that if one parent carriers the defective Huntington’s gene, his/her offspring have a 50/50 chance of inheriting the disease.
Huntington’s disease (HD) affects males and females equally and crosses all ethnic and racial boundaries. It typically begins in mid-life, between the ages of 30 and 45, though onset may occur as early as the age of 2. Children who develop the juvenile form of the disease rarely live to adulthood. There is a 50/50 chance of inheriting the fatal gene from the parents. Everyone who carries the gene will develop the disease. In Western countries, it’s estimated that about five to seven people per 100,000 are affected by HD.
There is no treatment or cure for Huntington’s Disease, and the patient eventually becomes completely dependent on others for daily functioning. Individuals may also die due to other secondary complications such as choking, infection, or heart failure. Children who are diagnosed with Huntington’s Disease do not usually live to reach adulthood.
- Australian Huntington’s Disease Association
- Huntington’s Disease Society of America
- Huntington Society of Canada
- Huntington’s Disease Association of Ireland
- International Huntington Association
* Control of hereditary disorders: Report of WHO Scientific meeting (1996)
** The molecular genetic epidemiology of cystic fibrosis (2004)